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ŠUMARSKI LIST 7-8/2022 str. 54     <-- 54 -->        PDF

ring series) responded with the same increasing or decreasing trend in tree-ring width compared to the previous year (Schweingruber 1983, Schweingruber et al. 1990). Pointer years were determined for the period for which meteorological data were available. For Scots pine, 1989 and 1997 were identified as positive pointer years and 1976, 1996, 2000, and 2011, as negative i.e. a total of six pointer years were identified. Regarding Austrian pine, 1989, 1997, and 2014 were identified as positive pointer years, and 1976, 2000, and 2003 as negative, i.e. a total of six pointer years.
Based on the characteristics and dendrochronological-statistical parameters of the analysed series of empirical values of radial growth of Scots pine and Austrian pine trees by site, it can be stated that the data related to the tree-ring width or radial growth made good material for chronology development in Zavidovići-Teslić area. The serial correlation between the empirical values and the master chronology of radial growth by site ranged from 0.288 to 0.438 for Scots pine and 0.391 to 0.560 for Austrian pine. Following the guidelines of Grissino-Mayer (2001), the values of the mean sensitivity were in the category of “intermediate”. In filtered (indexed) data, as expected, the effect of autocorrelation was practically eliminated, which was confirmed by autocorrelation coefficients close to zero.
Standardisation, i.e. the removal of the age-related trend from the tree-ring series was performed in the Arstan program. The coefficient of agreement (GLK) and t-value (tBP) showed similar patterns of tree rings in Scots and Austrian pine trees, i.e. matching of site chronologies was good enough to develop a master chronology of Scots pine and master chronology of Austrian pine for the Zavidovići-Teslić area. The determined parameters indicate that Austrian pine trees had a better matching of the obtained site chronologies and that the effect of mixedness did not manifest itself, i.e. no difference was found between pure and mixed stands.
A 145-year-old Scots pine master chronology and a 180-year-old Austrian pine master chronology were obtained. In the period from 1952 to 2014 (when the influence of climatic parameters was analysed), the values of the EPS coefficient (statistical measure showing the level of common signal among the samples used to obtain the chronology) were significantly above the lower limit of chronology certainty and reliability for both chronologies. According to Wigley et al. (1984), this limit amounts to 0.85.
Correlation analysis of the relationship between the radial growth index and precipitation and temperature in certain characteristic periods of the year revealed a negative effect of temperature (except in winter months) on the tree-ring formation in both species. In Scots pine, the dependence of the radial growth index on temperature was statistically significant for the period from June to August. Besides the same period, Austrian pine showed statistically significant dependence for September and October of the previous year and the growing season. The influence of winter temperatures was also statistically significant in Scots pine. In contrast to temperature, precipitation had a positive effect. Both tree species exhibited significant statistical dependence of radial growth on precipitation for the following periods: September and October of the previous year, June, July, and August, and the growing season. April and May were also significant in Austrian pine trees. As with temperature, there was little difference between the two species in terms of the influence of precipitation on the tree-ring formation, but we can conclude that the influence was generally more pronounced in Austrian pine.
The analysis of the temporal stability of the climate signal showed that the precipitation signal, in both species, exhibited a significant decline in the period from 1988 to 1991 and a growing trend in the last decade. Regarding the temperature signal, neither species had any significant increasing or declining trends in the past period, i.e. the signal was stable. Dendrochronological research of Austrian pine in the Northern Velebit National Park (Croatia) showed that the impact of precipitation was confirmed as stable and relatively high during the study period. Unlike precipitation, the temperature signal dropped significantly after 1996 (Miklić et al. 2021).
The determined value of the coefficient of correlation between the FAI index and the tree-ring width index for both Scots and Austrian pine was statistically significant and negative, which was to be expected because a higher value of the index indicates arid climate conditions (-0.46 for Scots pine and -0.54 for Austrian pine). In the study period, the study area had an average value of the FAI index of 4.86 (p = 0.05, confidence intervals: 4.42 and 5.29). According to Matović (2013), based on the value of this index, the upper and lower limits of the potential area of distribution were 2.97 and 6.10 for Austrian pine and 2.80 and 4.10 for Scots pine. The obtained average value and confidence interval of the FAI index indicates that Scots pine is an endangered species in the study area. The survival of Scots pine in these areas may be threatened by the changes expected to occur in the coming period and increase the drought index. Based on the climate and site conditions in the study area, we can conclude that Scots pine is close to its ecological threshold. Unlike Scots pine, Austrian pine grows in different climate conditions, and its distribution is primarily determined by other site conditions.
In the period from June to September for Austrian pine and June to August for Scots pine, high and statistically significant dependence of the tree-ring width index on the SPEI index pointed to the significant impact of moisture